The present invention relates in general to digital distribution of copyrighted content via an internetwork, and, more specifically, to secure distribution using multicasting.
Computer networks, such as the Internet, are becoming an important means for distributing digital content such as multimedia files. The multimedia content can include audio and video recordings such as music and feature films, respectively. The recordings may be for entertainment purposes or may be educational programs as part of a distance-learning educational system, for example.
In order to protect the rights of copyright owners of the distributed multimedia content, protection systems such as encryption and watermarking are used to restrict use of distributed content. Various digital rights management (DRM) models are being deployed to support Internet distribution of multimedia content. In general, content acquisition and license acquisition are separate operations. Thus, an encrypted file can be distributed to various end-users who will only be able to actually the view or listen to the content after separately obtaining an appropriate license. The grant of a license may depend upon authentication and authorization of a specific user and/or purchasing of the license. The granted license many include specific rules for the usage such as a limited number of times for playing the content or an expiration date.
The distribution of the multimedia file to numerous recipients (whether from a central distribution point or between end-users) within an internetwork can consume a large amounts of bandwidth. Packets or datagrams transported over a computer network for distributing content files protected using DRM are typically sent as unicast messages and wherein each copy of the distributed file is sent separately from point-to-point. Multicasting is a known the technique for distributing content more efficiently between a single content server and multiple recipients. However, many individual networks connected within the Internet are not multicast capable. Furthermore, DRM systems are oriented toward unicast distribution rather than multicast.
Multicasting can result in significantly more efficient use of overall network resources since multiple copies of the same information packets between any sender/receiver pair are avoided. Reduction in traffic loads can be especially significant in the network backbone.
In the IP protocol, multicast messages use reserved IP addresses (Class D) set aside for multicast groups. For example, a source server or host may distribute streaming multimedia (e.g., video and/or audio) or other information as datagrams specifying a particular multicast group number in the destination address. The datagrams propagate via multicast-enabled routers which typically maintain local group databases identifying next-hop routers and/or end user destinations that have requested receiving datagrams from the multicast group (i.e., that have joined). If a router's database identifies more than one destination for a multicast group, the router replicates the datagram and sends it to each destination.
When a router receives a join message for a multicast group that it is not currently receiving, then the router uses a multicast routing protocol such as Protocol-Independent Multicast (PIM) to create the necessary links from a source of the multicast stream to itself. When no longer needed, the router eliminates or prunes multicast distribution links to it that are no longer needed.
When distributing streams of multimedia content, the distributed content and the player can be configured to allow a user to join the multicast group while the stream is in progress and begin to view or listen to the content at an intermediate point. If, however, the content is encrypted using DRM then it has not been possible to obtain a license until at least the beginning portions of a particular file have been received.